Extrusion apparatus



EXTRUSION APPARATUS 3 Sheeis-$heet 1 Filed July 26, 1965 2 E 8. E E

as f r 22 a; a: g 3 21% A |\1 V m.\l/& 1 W v v H r J%% h M1 HE 2 w, 1 .E H g E E E .13. 3 E E 2 N2 Jan. 23, 1968 E. J. AVERILL ET AL 3,364,716

EXTRUSION APPARATUS Filed July 26, 1965 S Sheets-Sheet 2 150 172 119 151 152 F 166 L J 5m (-7 117 Jan. 23, 1968 E. J. AVERILL ET AL v I 3,364,716

EXTRUSION APPARATUS Filed July 26, 1965 3 Sheets-Sheet 5 United States Patent Otlice 3,354,716 Patented Jan. 23, 1958 3,364,716 EXTRUSION APPARATUS Eric John Averill, Churchdown, and Derek Green, Lytham Saint Annes, England, assignors, by mesne assignments, to Fielding & Platt Limited, Gloucester, England Filed July 26, 1965, Ser. No. 474,926 Claims priority, application Great Britain, July 7, 1965, 28,823/65 2 Ciaims. (Cl. 72-253) ABSTRACT OF THE DISCLOSURE The invention is concerned with providing an extrusion press in which the processes of hydrostatic and mechanical extrusion are combined. More specifically the billet is subjected to forces derived firstly from the pressurisation of liquid in a chamber surrounding the billet and secondly from a mechanical axial loading applied thereto in a direction towards the die. In an embodiment of the invention the press is provided with a plunger formed with a passageway connecting the liquid pressure cylinder and the extrusion chamber, the passageway affording transmission of pressure from the liquid in the cylinder to liquid surrounding the billet in the extrusion chamber. A pressure differential is maintained between the ends of the plunger which forces the latter to apply a mechanical axial loading on the billet in a direction towards the die.

This invention relates to extrusion processes and in particular to hydrostatic extrusion processes. In a conventional extrusion process a billet held within a chamber is subjected to a direct mechanical loading to extrude the billet from the chamber through a die. The billet is a close fit in the chamber and extrusion pressure is applied on the end face of the billet by a ram operating in the bore of the chamber. Hydrostatic extrusion has several advantages over conventional extrusion and differs from conventional extrusion in that a liquid is used to apply extrusion pressure on the billet. The liquid envelops the billet in the chamber and is pressurised to act directly on the billet. Because the liquid envelops the billet there is no frictional contact between the chamber and the billet. Die friction is also reduced because the pressurised fluid adjacent the throat of the die provides hydrodynamic lubrication between the extruding material and the die.

In hydrostatic extrusion the material of the billet is subjected to a hydrostatic stress system but it is the axial component of stress acting in the billet in the direction towards the die orifice and the consequent radial reaction at the die throat which results in extrusion of the material of the billet through the die.

The axial component of stress set up in the billet and hence the forces acting to extrude the material of the billet through the die is dependent on the pressure applied in the liquid surrounding the billet. The degree of pressure which must be applied in the liquid to cause extrusion depends on the yield stress of the material to be extruded.

In the case of material having a very high yield stress the pressure required in the liquid to effect hydrostatic extrusion may be prohibitively high because of the difficulties arising from containment of liquids subjected to such high pressure. These difi'zlculties can be overcome by operation of the hydrostatic extrusion process so that the billet, as well as being subjected to a hydrostatic stress system by the pressurisation of liquid in a chamber surrounding the billet, is also subjected to a direct mechanical axial loading in a direction towards the extrusion die. In this process the axial component of stress in the billet, which as explained above is responsible for the forces resulting the billet through the die. However as the direct mechanical axial loading applied to the billet supplements the axial component of hydrostatic stress set up in the billet due to the pressure in the liquid enveloping the billet, a total axial stress component of the magnitude required to eifect extrusion is produced in the billet using a much lower pressure in the liquid enveloping the billet than is required in the liquid for operation of a purely hydrostatic extrusion process.

In this process the problems arising from the use of very high liquid pressures which are necessary for the hydrostatic extrusion of materials having a high yield stress are avoided whilst the advantages inherent in the hydrostatic extrusion process are retained.

Apparatus for carrying out the process comprises an extrusion chamber having a bore with an extrusion die at one end, means for pressurising hydraulic liquid in the bore of the etxrusion chamber about a billet contained therein, a plunger entered into the bore of the extrusion chamber at its other end, means for loading the plunger to apply a mechanical axial loading on the billet in the extrusion chamber and means for bleeding hydraulic liquid from the bore of the extrusion chamber as extrusion proceeds so that the plunger remains in contact with and maintains a mechanical axial loading on the billet during extrusion of the billet.

In a particular form of apparatus as described above the plunger has a head outside the bore of the extrusion chamber of larger cross sectional area than the cross sectional area of the body of the plunger, the head of the plunger coupling with a cylinder, a passageway being provided leading through the plunger from the cylinder to the bore of the extrusion chamber, means being provided for pressurisation of liquid in the cylinder to act on the head of the plunger, and force the plunger to apply a mechanical axial loading on the billet, the passageway leading through the plunger providing for transmission of pressure from the liquid in the cylinder to liquid in the extrusion chamber about a billet contained therein and the passageway also providing for bleeding of liquid from the bore of the extrusion chamber into the cylinder as extrusion proceeds and the plunger moves into the bore of the extrusion chamber in contact with the billet.

In this form of apparatus the cylinder may be blind ended with the head of the plunger sliding in the bore of the cylinder, liquid being pressurised in the bore of the cylinder to act on the head of the plunger by external loading of the cylinder.

Alternatively the head of the plunger may be in fixed engagement with one end of the bore of the cylinder, which is movable with the plunger, liquid being pressurised in the bore of the cylinder to act on the head of the plunger by a ram entered into the bore of the cylinder from its other end.

In operation of apparatus of the particular forms de scribed above the free space in the cylinder and in the extrusion chamber surrounding a billet contained therein are filled with hydraulic liquid. The passageway leading through the plunger from the cylinder to the extrusion chamber provides that when the hydraulic liquid in the cylinder is pressurised, the hydraulic liquid in the extrusion chamber surrounding the billet is subjected to the same degree of pressurisation. The body of the plunger in the extrusion chamber bears against the end of the billet and the pressure of the hydraulic liquid in the cylinder acting on the larger area of the head of the plunger forces the plunger to apply a mechanical axial loading on the billet. The axial component of stress produced in the billet due to the combined effect of the hydrostatic pressure applied on the billet and the mechanical axial loading of the plunger on the billet gives rise to forces at the die causing extrusion of the billet from the extrusion chamber through the die.

As extrusion proceeds the billet remains the same diameter but reduces in length in the extrusion chamber. The plunger moves into the bore of the extrusion chamber as extrusion proceeds and maintains contact with the end of the billet so that the mechanical axial loading of the plunger on the billet is applied throughout the extrusion process. As the plunger moves into the bore of the extrusion chamber in contact with the end of the billet during extrusion, hydraulic liquid is transferred from the extrusion chamber into the cylinder through the passageway leading through the plunger.

In the above particular forms of apparatus the amount of mechanical axial loading applied on the billet is directly dependent on the pressure applied commonly in the hydraulic liquid acting in the cylinder on the head of the plunger and in the extrusion chamber on the billet. The mechanical axial loading applied on the billet cannot be varied without varying the pressure in the hydraulic liquid.

It is an object of the present invention to provide means in such apparatus whereby the amount of axial mechanical loading applied on the billet can be varied independently of the pressure applied in the hydraulic liquid acting in the cylinder on the head of the plunger and in the extrusion chamber on the billet.

According to the present invention extrusion apparatus comprises an extrusion chamber having a bore with an extrusion die mounted at one end of the bore, a plunger entered into the bore of the extrusion chamber at its other end, the plunger having a head of larger cross sectional area than the cross sectional area of the plunger, the head of the plunger coupling with a cylinder, a passageway defined in the plunger leading from the cylinder to the bore of the extrusion container, means for pressurisation of liquid in the cylinder to act on the head of the plunger and force the plunger to apply a mechanical axial loading on a billet contained in the extrusion chamber, liquid in the extrusion chamber about the billet being pressurised through the passageway in the plunger, adjustable loading means being provided acting in opposition to the loading applied on the plunger by pressurisation of liquid in the cylinder so as to counteract a selected amount of the mechanical axial loading applied on the billet by the plunger.

In one form of this apparatus a fluid actuated piston and cylinder arrangement is provided acting on the plunger in opposition to the loading applied on the plunger by the pressure of hydraulic liquid acting in the cylinder on the head of the plunger.

The invention will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a longitudinal sectional elevation of an extrusion press in accordance with the invention,

FIGURE 2 is a cross sectional elevation, the right hand half of the figure being a section along the line AA in FIGURE 1 and the left hand half of the figure being a section along the line BB in FIGURE 1,

FIGURE 3 is a cross sectional elevation, the right hand half of the figure being a section along the line CC in FIGURE 1 and the left hand half of the figure being a section along the line D-D in FIGURE 1,

FIGURE 4 is a detail of the area within the chain dotted circle IV in FIGURE 1,

FIGURE 5 is a detail of the area within the chain dotted circle V in FIGURE 1.

The press shown in FIGURES 1-5 of the drawings comprises a massive cast steel head frame 101 and a main cylinder support housing 102 joined by three heavy steel shafts 103. The main cylinder support housing 102 consists of two end plates 104 joined by transverse stiffening plates 105. Massive nuts 106 on the threaded ends of the steel shafts 103 locate the head frame 101 and the main cylinder support housing 102 in spaced relationship.

As shown in FIGURES 2 and 3 the head frame 101 and the main cylinder support housing 102 are carried on the floor by welded frames 107.

A main hydraulic ram 108 operates in a large cylinder 109 which is welded in the support housing 102. The ram 108 is sealed in the cylinder 109 by a sealing ring 110 and the cylinder 109 has a gunmetal lining sleeve 111. The nose of the ram 108 is fitted by a cross head 112 which as shown in FIGURE 2 is connected with shafts 113 with two auxiliary double acting power save/ drawback cylinders 114 mounted in the main cylinder support housing '102. The cross head 112 has integral support lugs 115 fitted with bearing pads 115a which run on slides 116 carried by frames 117 bolted to the floor. A plunger 118 is mounted in an adaptor bush 119 bolted to the face of the crosshead 112. The plunger 118 has a head 120 which is held by an externally threaded ring 121 screwed into the adaptor bush 119 carried by the crosshead 112. The plunger 118 is entered into the bore of a pressurisation cylinder 123 which as shown in cross section in FIGURE 2, is of double ring construction comprising an inner ring 124 shrink fitted in an outer ring 125. The cylinder 123 is fitted with a flanged adaptor sleeve 126 which is bolted to a locating flange 127 engaged in a groove 128 around the cylinder 123. A crosshead 129 is fitted on the adaptor sleeve 126 bearing against an integral flange 130 of the adaptor sleeve 126. A flanged bush 131 is mounted on the end face of the cylinder 123 by bolts 132 screwed into the crosshead 129. The crosshead 129 is connected by shafts 133 with two auxiliary cylinders 134 mounted in the main cylinder support structure 102. The auxiliary cylinders 134 are double acting. The shafts 133 have piston heads 135 sealed by packings 136 in the cylinders 134. The shafts 133 are sealed on entry into the cylinders 134 by packings 137. Each shaft 133 is connected with the crosshead 129 by a nut 138 and a locating bush 139 bearing against a step 140 on the shaft 133. As shown in FIGURE 2 the crosshead 129 has integral mounting lugs 141 and 142, the lugs 141 being fitted with bearing pads 141a which run on the slides 116 carried by the frames 117 to sup port the cylinder 123 vertically and the lugs 142 being fitted with bearing pads 142a which run on slides 143 also carried by the frames 117 to locate the cylinder 123 laterally. As shown in the detail of FIGURE 4 the plunger 118 is sealed in the bore of the cylinder 123 by a copper mitre ring 144 and a rubber O-ring 145.

A plunger 146 is fitted in the bush 131 in sealed engagement with the bore of the cylinder 123, the plunger 146 having a head 147 which is clamped by an externally threaded ring 148 screwed into the bush 131. Sealing of the plunger 146 in engagement with the bore of the cylinder 123 is by means of a mitre ring and O-ring seal fitted on a stepped part 149 of the plunger head 147 which fits inside the end of the bore of the cylinder 123.

The plunger 146 is entered into the bore of an extrusion chamber 150 of smaller internal diameter than the internal diameter of the cylinder 123. As shown in cross section in FIGURE 3 the extrusion chamber 150 is of double ring construction, comprising an inner ring 151 shrink fitted in an outer ring 152. The extrusion chamber 150 is fitted with an adaptor sleeve 153 which is located by a step 154 on the outer ring 152 of the chamber 150 and a locating flange 155 fitted in a groove 156 around the outer ring 152 of the chamber 150.

A cross head 157 is fitted on the adaptor sleeve 153 located between an external flange 158 on the adaptor sleeve 153 and a flange 159 fitted in a groove 160 around the adaptor sleeve 153. The crosshead 157 is connected by shafts 161 with two double acting extrusion chamber shift cylinders 162 mounted on the head frame 101 of the machine. Each shaft 161 is connected with the crosshead 157 by a nut 163 and a bush 164 bearing against a step 165 on the shaft 161. As shown in FIGURE 3 the crosshead 157 has integral mounting lugs 166 and 167, the lugs 166 being fitted with hearing pads 166a which run, on the slides 116 carried by the frame 117 to support the extrusion chamber 150 vertically and the lugs 167 being fitted with bearing pads 167a which run on the slides 143 carried by the frames 117 to locate the extrusion chamber 150 laterally. As shown in FIGURE 5 the plunger 146 is sealed in the bore of the extrusion chamber 150 by a copper mitre ring 168 and a rubber O-rin g 169. A passageway 17 0 through the plunger 146 leads from the bore of the pressurisation cylinder 123 into the bore of the extrusion chamber 150.

A die slide 171 operated by a double acting cylinder 172 is movable transversely in the head frame 107 along guide surfaces 173.

For certain applications of the press a shear cylinder assembly 174 is mounted on the head frame 101 above the die slide 171.

A back pressure tube 175 extends rearwardly out of the head frame 101 in axial alignment with the bore of the extrusion chamber 150.

Hydraulic liquid for operation of the various hydraulic cylinders in the machine is supplied by a pump 176 driven by a motor 177. Hydraulic liquid is supplied to the cylinder 111 through a prefilling valve 178.

As shown in FIGURES 1 and 5 a parallel sided die 17 9 is located in the die slide 171. A billet 180 to be extruded is held in the extrusion chamber 150, the billet 180 being fitted with a disposable shear ring 181 which is sealed in the bore of the extrusion chamber 150 by a copper mitre ring 182 and a rubber O-n'ng 133. The die 179 is sealed against the disposable shear ring 152 by a copper mitre ring 184.

In one application the press is operated to extrude the billet 180 through the die 179 into ambient atmospheric pressure in the back pressure tube 175. The press is ready for loading of the billet 180 with the main ram 108 and the pressurisation cylinder 123 drawn back to their extreme right hand positions in the press and with the extrusion chamber 150 moved back from the die 179 so that a space exists behind the die 179 to allow access to the bore of the extrusion chamber 150 at its front end face. The billet 180, having been fitted with the shear ring 181 and its sealing rings 1'82 and 183 is swung on a billet charger into the space between the die 179 and the extrusion chamber 150 so that the billet 180 is brought into axial alignment with the bore of the extrusion chamber 150. The main ram 108 is now moved slowly forward by the auxiliary power save cylinders 1. 14 and the pressurisation cylinder 123 is moved forward simultaneously with the main ram 108 by the auxiliary cylinders 134. The main ram 108 and the pressurisation cylinder 123 are moved forward until the face of the plunger 146 contacts the rear end face of the billet 180 and pushes the billet 180 into engagement with the die 179. As the billet 180 is held between the die 179 and the face of the plunger 146 the billet charger can now be removed. The main ram 108 and the pressurisation cylinder 123 are now held stationary and the extrusion chamber 150 is moved over the billet 180 by the extrusion chamber shift cylinders 162 until sealing is effected between the shear ring 181 and the copper mitre ring 184 at the end face of the die 179.

At this stage the press is in the condition shown in draulic liquid from the pressurisation cylinder 123 through the longitudinal passageway 170 in the plunger 146 into the extrusion chamber 150. Further forward movement of the main ram 108 causes pressurisation of the hydraulic liquid in the pressurisation cylinder 123 and in the extrusion chamber surrounding the billet 180.

The pressure of the hydraulic liquid acting on the end face of the plunger 146 in the pressurisation cylinder 123 forces the pressurisation cylinder 123, and the plunger 146 forward so that the plunger 146 applies a mechanical axial loading on the billet 180.

The axial component of stress produced in the billet 186 due to the combined efi'ect of the hydrostatic pressure of the liquid acting on the billet 180 in the extrusion chamber 150 and the axial mechanical loading of the plunger'146 on the billet gives rise to forces at the die 179 causing extrusion of the billet 180 from the extrusion chamber 150 through the die 179. As extrusion proceeds the pressurisation cylinder 123 moves forward so that the plunger 146 remains in contact with the billet and maintains the mechanical axial loading in the billet. During extrusion as the plunger 146 moves forward in contact with the billet, liquid is transferred from the extrusion chamber 150 through the passageway in the plunger 146 into the pressurisation cylinder 123, the pressurisation cylinder 123 moving forward relatively to the plunger 118 carried by the main ram 108.

The degree of mechanical axial loading applied on the billet by the plunger 146 can be adjusted by holding back the pressurisation cylinder 123 by means of the auxiliary cylinders 134. Maximum mechanical axial loading on the billet, dependent on the degree of pressure applied in the hydraulic liquid, is applied when the pressurisation cylinder 12 3 is free to move independently of the auxiliary cylinders 134. To reduce the mechanical axial loading applied on the billet by the plunger 146, the forward force acting on the pressurisation cylinder 123 is reduced by applying a backwards force on the pressurisation cylinder 1 2 3 by means of the auxiliary cylinders 1 34. The mechanical axial loading applied on the billet can be adjusted within the range from full loading, where no back force is applied to the pressurisation cylinder 123, to zero mechanical loading, where the back force applied to the pressurisation cylinder 123 just balances the forward force acting on the cylinder 123. In this latter case the billet is subjected to simple hydrostatic extrusion.

:Extrusion is carried out until the face of the plunger 14-6 reaches the shear ring 181 (a limit switch may be provided to indicate when this position is reached). The main cylinder 109 is now connected to exhaust and the pressure of the hydraulic liquid in the pressurisation cylinder 123 drops to near normal. Any remaining slight excess of pressure in the hydraulic liquid is reduced by slight withdrawal of the main ram 108 using the power save cylinders 114.

With the pressurisation cylinder 123 remaining fixed so that the billet discard and the disposable shear ring 181 are held by the plunger 146 against the die 179, the extrusion chamber 150 is moved back over the plunger 146 using the extrusion chamber shift cylinders 16 2. When the billet discard and disposable shear ring 181 are out of the extrusion chamber 150, the extrusion chamber 150, the pressurisation cylinder 12 3 and the main ram 108 are moved back simultaneously to their extreme right hand positions in the press using the extrusion chamber shift cylinders 162, the auxiliary cylinders 134 and the power save/draw back cylinders 114 respectively. The shear cylinder assembly 174 is now operated to shear off the discard end of the billet at the disposable shear ring 181 and the extruded rod is withdrawn through the back end of the back pressure tube 175. The press is now in condition for charging of a further billet. For a hard material, which it is not possible to shear a circular saw may be used in place of the shear cylinder assembly 174 for cutting off the discard end of the billet.

As an alternative to the use of the shear cylinder assembly 174 for shearing off the discard end of a billet of a soft material the shearing may be done using the die slide 171. In this event, after extrusion, the die slide 171 is operated after moving the extrusion chamber 150 to expose the billet discard so that shearing of the extrusion occurs behind the die 179. The die slide 171 then moves the die 179 fully over to the out position and the severed discard end of the billet and die is then removed from the die slide 171 and replaced with a new die.

In the latter case where the extrusion is sheared off by means of the die slide 171 a conventional conically throated die may be used and the disposable shear ring 181 dispensed with.

The press can also be employed to extrude a billet through the die 179 into hydraulic liquid under pressure in the back pressure tube 175. Extrusion into a liquid under pressure is particularly applicable to brittle materials as this avoids cracking in the extruded product. As in the application described above, wherein the billet is extruded into atmospheric pressure in the back pressure tube 175, the press is ready for loading of the billet with the main ram 108 and the pressurisation cylinder 123 drawn back to their extreme right hand positions in the press and with the extrusion chamber 150 moved back from the die 179 to provide a space forward of the chamber 150 for charging of the billet. 'Ihe billet fitted with the shear ring 181 and sealing rings 182 and 183, is brought on the billet charger into axial alignment with the bore of the extrusion chamber 150. The main ram 108 and the pressurisation cylinder 123 are moved forward simultaneously by the power save cylinders 114 and the auxiliary cylinders 134 respectively until the face of the plunger 146 contacts the billet and pushes the billet into loose engagement with the die 179. The main ram 108 and the pressurisation cylinder 123 are now held stationary and the extrusion chamber 150 is moved over the billet by the extrusion chamber shift cylinders 162 until scaling is effected between the shear ring 181 and the copper mitre ring 184 at the end face of the die 179.

At this stage the press is in the condition shown in FIG- URE 1. The pressurisation cylinder 123 is now pulled back by means of the auxiliary cylinders 134 so that the plunger 146 is withdrawn from contact with the end face of the billet in the extrusion chamber 150, the main ram 108 being held steady by the auxiliary power save cylinders 114. A valve is now opened to a slightly pressurised container of hydraulic liquid which is thereby connected through a longitudinal duct in the plunger 118 with the pressurisation cylinder 123. The hydraulic liquid feeds through the longitudinal duct in the plunger 118 to fill the pressurisation cylinder 123, the extrusion chamber 150 (through the longitudinal passageway 170- in the plunger 146) and the back pressure tube 175 from the extrusion chamber 150. The valve to the container of hydraulic liquid is now closed and the main ram 108 is moved forward under main power whilst the pressurisation cylinder 123 is held back by means of the auxiliary cylinders 134. The plunger 118 moving forward in the bore of the pressurisation cylinder 123 pressurises the hydraulic liquid in the pressurisation cylinder 123, the extrusion chamber 150 and the back pressure tube 175. The pressure is brought up to that required in the back pressure tube 175. Hold back of the pressurisation cylinder 123 by the auxiliary cylinder 134 is now released so that the pressurisation cylinder 123 moves forward until the plunger 146 contacts the end face of the billet in the extrusion chamber 150 and forces the billet into sealing engagement with the die 179. Extrusion of the billet is now carried out by advancing the main ram 108 so as to raise the pressure of the hydraulic liquid in the pressurisation cylinder 123 and the extrusion chamber to the level required for extrusion. Extrusion proceeds under the combined effect of the hydrostatic pressure of the hydraulic liquid and the mechanical axial loading applied on the billet by the plunger 146. In this application also the degree of mechanical axial loading applied on the billet by the plunger 146 can be adjusted by holding back the pressurisation cylinder 123 by means of the auxiliary cylinders 134. Again extrusion is continued until the face of the plunger 146 reaches the shear ring 181. During extrusion excess hydraulic liquid is exhausted from the back pressure tube through a bleed valve which keeps the pressure of the hydraulic liquid in the back pressure tube 175 constant during extrusion and allows reduction of the pressure in the back pressure tube 175 to normal at the end of extrusion.

At the end of extrusion, pressure in the back pressure tube 175 is first reduced to normal and then the main cylinder 109 is exhausted so that pressure in the pressurisation cylinder 123 and the extrusion chamber 150 falls to about normal. Again any remaining slight excess of pressure in the hydraulic liquid in the pressurisation cylinder 123 and the extrusion chamber 150 is reduced by slight withdrawal of the main ram 108. With the pressurisation cylinder 123 remaining fixed the extrusion chamber 150 is moved back over the plunger 146 to expose the billet discard and the disposable shear ring 181. The extrusion chamber 150, the pressurisation cylinder123 and the main ram 108 are then moved back to their extreme right hand positions in the press. The shear cylinder assembly 174 is now operated to shear off the discard end of the bitlet at the disposable shear ring 181 and the extruded rod is withdrawn through the back end of the back pressure tube 175.

Alternatively as described above the discard end of a billet of soft material may be sheared by means of the die slide 171, or the discard end of a billet of hard material may be cut off using a rotary saw.

We claim:

1. Extrusion apparatus comprising an extrusion chamber having a bore with an extrusion die mounted at one end of the bore, a plunger entered into the bore of the extrusion chamber at its other end, the plunger having a head of larger cross sectional area than the cross sectional area of the plunger, the head of the plunger coupling with a cylinder, a passageway defined in the plunger leading from the cylinder to the bore of the extrusion chamber, means for pressurisation of liquid in the cylinder to act on the head of the plunger and force the plunger to apply a mechanical axial loading on a billet contained in the extrusion chamber liquid in the extrusion chamber about the billet being pressurised through the passageway in the plunger, adjustable loading means being provided acting in opposition to the loading applied on the plunger I by pressurisation of liquid in the cylinder so as to coun- References Cited UNITED STATES PATENTS 796,970 8/1905 Hoopes 72253 2,558,035 6/1951 Bridgman 7260 3,126,096 3/ 1964 Gerard 72253 CHARLES W. LAN HAM, Primary Examiner.

K. C, DECKER, Assistant Examiner. 

